1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic head for perpendicular magnetic recording that is used for recording data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a method of manufacturing a magnetic head for perpendicular magnetic recording that has a shield provided around a main magnetic pole.
2. Description of the Related Art
Recently, magnetic recording devices such as a magnetic disk drive have been improved in recording density, and magnetic heads and magnetic recording media of improved performance have been demanded accordingly. The recording systems of magnetic recording devices include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. As compared with the longitudinal magnetic recording system, the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density.
Magnetic heads for perpendicular magnetic recording typically have, as do magnetic heads for longitudinal magnetic recording, a structure in which a reproducing head including a magnetoresistive element (hereinafter, also referred to as an MR element) for reading and a recording head including an induction-type electromagnetic transducer for writing are stacked on a substrate. The recording head includes a main magnetic pole that produces a magnetic field in the direction perpendicular to the plane of the recording medium. The main magnetic pole has an end face located in a medium facing surface that faces the recording medium. To increase the recording density, reduction in track width and improvement in recording characteristics, such as overwrite property which is a parameter indicating an overwriting capability, are required of the recording head of the perpendicular magnetic recording system.
A magnetic head for use in a magnetic disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is configured to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits a better capability of writing on a recording medium compared with the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already recorded on one or more tracks that are adjacent to a track targeted for recording are erased or attenuated when recording a signal on the track targeted for recording (such a phenomenon will be hereinafter referred to as adjacent track erase). To increase the recording density, it is required to suppress the adjacent track erase.
One of known techniques for increasing the recording density is to provide a shield having an end face that is located in the medium facing surface and wraps around the end face of the main magnetic pole (such a shield will be hereinafter referred to as a wrap-around shield), as described in U.S. Pat. No. 5,075,956 and U.S. Pat. No. 6,954,340 B2, for example. A gap is provided between the main magnetic pole and the wrap-around shield. The wrap-around shield takes in a magnetic flux that is generated from the end face of the main magnetic pole located in the medium facing surface and that expands in directions other than the direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. The wrap-around shield includes a lower shield that is located closer to the air-inflow end of the slider relative to the main magnetic pole, an upper shield that is located closer to the air-outflow end of the slider relative to the main magnetic pole, and first and second side shields that are located on opposite sides of the main magnetic pole in the track width direction. The gap includes a lower gap that is interposed between the main magnetic pole and the lower shield, an upper gap that is interposed between the main magnetic pole and the upper shield, and two side gaps that are interposed between the main magnetic pole and the two side shields. According to this technique, the lower shield and the upper shield serve to increase the gradient of the recording magnetic field, and the two side shields serve to suppress adjacent track erase. Increasing the recording density is made possible by these functions.
Here, a method of forming the wrap-around shield will be discussed. A possible method of forming the wrap-around shield is as follows. First, the lower shield is formed on an underlayer for the lower shield. Next, an initial lower gap layer, which is intended to later become the lower gap, is formed on the lower shield. Next, the main magnetic pole is formed on the initial lower gap layer. Next, an initial side gap layer including the two side gaps is formed to cover the entire main magnetic pole and the top surface of the initial lower gap layer. Next, a mask is formed to cover the entire main magnetic pole and a part of the initial side gap layer. The mask is formed by patterning a photoresist layer by photolithography, for example. Next, the other part of the initial side gap layer which is uncovered with the mask and a part of the initial lower gap layer lying below that part of the initial side gap layer are removed by etching. This exposes a part of the top surface of the lower shield and makes the remaining initial lower gap layer into the lower gap. Next, the two side shields, the upper gap, and the upper shield are formed.
In the foregoing method of forming the wrap-around shield, etching the respective parts of the initial side gap layer and the initial lower gap layer using the foregoing mask forms a structure that includes the lower gap having a width greater than that of the main magnetic pole, and the main magnetic pole and the initial side gap layer which are arranged on the lower gap. In such a structure, the initial side gap layer includes two portions that lie on the top surface of the lower gap at positions on opposite sides of the main magnetic pole in the track width direction.
The foregoing method of forming the wrap-around shield has two problems as described below. A first problem is that the lower gap and the two portions of the initial side gap layer lying on the top surface of the lower gap create two corner parts near the bottom surface of the main magnetic pole, the two corner parts being formed between respective two intersecting surfaces at, e.g., right angles, and the two corner parts can induce adjacent track erase. More specifically, if such two corner parts are created, then two recesses are formed in the two side shields along the two corner parts. Magnetic fluxes emerging from the recording medium and from the main magnetic pole tend to concentrate in the vicinities of the two recesses, and this can induce adjacent track erase.
A second problem is that the center of the mask in the track width direction can deviate from the center of the main magnetic pole in the track width direction, so that the effects of the two side shields become non-equal. More specifically, when the center of the mask in the track width direction deviates from the center of the main magnetic pole in the track width direction, the center of the lower gap in the track width direction deviates from the center of the main magnetic pole in the track width direction. Then, the distance between the surface of the first side shield in contact with one of the side surfaces of the lower gap and the center of the main magnetic pole in the track width direction differs from the distance between the surface of the second side shield in contact with the other side surface of the lower gap and the center of the main magnetic pole in the track width direction. This makes the effects of the two side shields not equal, and can thus cause a deterioration of the characteristics of the magnetic head.